Moraxella (Branhamella) catarrhalis is a Gram-negative diplococcus that causes respiratory tract infections in humans. M. catarrhalis is now accepted as the third most common cause of otitis media in infants and children, after Streptococcus pneumoniae and Haemophilus influenzae. M. catarrhalis has also been associated with several other types of infection, including sinusitis, persistent cough, acute laryngitis in adults, suppurative keratitis, conjunctivitis neonatorum, and invasive diseases in the immunocompromised host.
Since approximately 90% of M. catarrhalis strains are resistant to antibiotics (β-lactamase positive) and that recurrent otitis media is associated with high morbidity, there is a need for the development of a vaccine that will protect hosts from M. catarrhalis infection. An infection by M. catarrhalis induces an immune response against antigens found at the surface of the bacterial cells. However, many of these surface proteins are still not characterized, nor has the immune response resulting in protection from infection by different strains been determined.
To develop a vaccine that will protect hosts from M. catarrhalis infection, efforts have mainly been concentrated on outer membrane proteins such as the high-molecular-mass protein named ubiquitous surface protein A (UspA). This protein is considered a promising vaccine candidate because a monoclonal antibody and polyclonal antibodies were both shown to be bactericidal and protective in the murine pulmonary-clearance model. However, this protein was shown to be highly variable among the different strains of M. catarrhalis. In addition to this protein, other M. catarrhalis proteins have generated interest as potential vaccine candidates. The transferrin-binding protein which possesses conserved epitopes exposed on the bacterial surface. However, there was divergence in the degree of antibody cross-reactivity with the protein from one strain to another. Other investigators have also focused on the 45-kDa protein CD (OMP CD). This protein is highly conserved among strains of M. catarrhalis, however adults with chronic obstructive pulmonary disease show variability in the immune response against the OMP CD.
Therefore there remains an unmet need for M. catarrhalis polypeptides which may be used to prevent, diagnose and/or treat Moraxella (Branhamella) catarrhalis infection.